This invention relates to compressor and turbine wheel shaft seals, particularly for use in engine turbochargers and the like. More particularly, the invention relates to a shaft seal system especially applicable to four cycle engine turbochargers.
Well known turbocharged two cycle diesel engines have been used in railway locomotives and other applications for many years. Because two cycle engines are not self scavenged, a turbocharger has been developed which uses a mechanical drive train to drive a turbine/compressor rotor to provide adequate scavenging and charging air pressure at engine idle and in the lower speed and power settings of the associated engine. The turbocharger is provided with turbine and compressor rotor shaft seals employing labyrinth seal grooves fed with pressure air from the output of the compressor wheel. The developed labyrinth seal system has proved to be extremely reliable and functionally effective, as well as cost effective for use in two cycle engine applications. The labyrinth seal grooves are preferably formed in an inner cylinder surrounding the rotor shaft, although they could alternatively be formed in an outer cylinder rotating with the shaft.
In designing a turbocharger for a four cycle diesel locomotive engine, the labyrinth seal system used in the two cycle engine turbocharger has been found to be less effective. This is because, at idle and in operation at light loads, the four cycle turbocharger does not provide sufficient air pressure boost to supply adequate air pressure to the labyrinth seals. A suitable cost effective and reliable seal system was therefore desired to effectively limit oil leakage under the full operating range of the four cycle engine and turbocharger.
The present invention provides an improved seal system including a dual phase seal for limiting leakage from lubricated rotor support bearings to a turbine and/or compressor wheel of a rotor operational over an extended speed range. The dual phase seal combines features of the previously developed labyrinth seal, effective in a higher portion of the turbocharger rotor speed range, with added features of a known auger seal, found to be effective in a lower portion of the rotor speed range.
In general, the dual phase seal includes an outer cylinder on the rotor between a bearing and an associated wheel, an inner cylinder carried by a rotor support and surrounding the outer cylinder with close clearance, auger seal grooving formed in one of the cylinders on a portion thereof toward the as bearing, labyrinth seal grooving formed in one of the cylinders on a portion thereof toward the wheel, and a pressure air supply to the labyrinth seal at a pressure which is reduced at rotor speeds in a lower portion of the speed range.
The seal system for a turbocharger includes a pressure air supply from an output of the compressor wheel to the labyrinth seal grooving of bearing seals for both the turbine and compressor ends of the rotor shaft. The auger groove portions of the dual phase seals provide effective sealing at lower rotor speeds but lose effectiveness at higher speeds. The labyrinth groove portions of the seals provide effective sealing at the higher rotor speeds where the auger seal portions are less effective.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.